Steam-Enhanced Calcium Looping Cycles with ... - ACS Publications

May 8, 2013 - School of Applied Sciences, Cranfield University, Cranfield MK43 0AL, ... in the carbonation gas stream (20% CO2, 15% steam or 0% steam,...
12 downloads 0 Views 425KB Size
Article pubs.acs.org/IECR

Steam-Enhanced Calcium Looping Cycles with Calcium Aluminate Pellets Doped with Bromides Vasilije Manovic,† Paul S. Fennell,‡ Mohamad J. Al-Jeboori,‡ and Edward J. Anthony*,§ †

CanmetENERGY, Natural Resources Canada, 1 Haanel Drive, Ottawa, Ontario, Canada K1A 1M1 Department of Chemical Engineering, Imperial College, London SW7 2AZ, United Kingdom § School of Applied Sciences, Cranfield University, Cranfield MK43 0AL, United Kingdom ‡

ABSTRACT: This study explores the effect of calcium bromide (CaBr2) doping of lime-based sorbents in the presence of steam during calcination/carbonation cycles. Two sorbents were tested: natural limestone (Cadomin, Canada) and a synthetic sorbent (pellets) prepared from Cadomin limestone with addition of calcium aluminate cement. The mixture of calcined limestone and cement was pelletized in a mechanical granulator that uses spray water as the part of the pelletization process. Both the original limestone and the prepared pellets were impregnated with a dilute CaBr2 solution to achieve a Ca/Br mole ratio of 500:1. The CO2 carrying activities of the sorbents were tested during calcination/carbonation cycles in a thermogravimetric analysis (TGA) apparatus. Realistic calcination conditions during the reaction cycles were employed: 900 °C with a CO2 sweep gas. Multicycle tests were carried out with steam 15% and without steam present in the carbonation gas stream (20% CO2, 15% steam or 0% steam, N2 balance in both cases). The results showed that doping with CaBr2 has a beneficial effect on sorbent CO2 capture activity, and in particular, the conversion rate during the diffusion-controlled stage of carbonation was found to exhibit a strong synergic enhancement in the presence of steam. The effects of doping and steam were more pronounced in the case of synthetic pellets, resulting in an uptake of 23.8 g of CO2/100 g of sorbent after 31 cycles, which represents a conversion of 35.6%. This CO2 capture uptake is very high compared with that of pellets with no CaBr2 addition and no steam present during the reaction cycles, where only 15.0 g of CO2/100 g of sorbent (22.5% conversion) was seen after 10 cycles. These results suggest that the preparation of synthetic sorbents for calcium looping using solutions containing small amount of bromides would be beneficial in practical applications, and steam will either be produced by firing almost any fuel or be found in flue gas suitable for processing by calcium looping.

1. INTRODUCTION Lime-based sorbents have been intensively investigated as sorbents for CO2 capture in looping cycle processes for CO2 capture from large-scale sources to reduce CO2 emissions to the atmosphere and mitigate related climate changes.1,2 Calcium looping (CaL) cycles are based on a heterogeneous gas−solid reaction (carbonation) with the formation of a solid product (CaCO3)

CaCO3 given that the molar volumes of CaCO3 and CaO are 37 and 17 cm3/mol, respectively. However, this is not normally the true limit because the conversion reached after the first carbonation of natural limestone is usually only 70−80% of that limit, and during further cycles, the conversion monotonically decreases, reaching values of 10 g/100 g of sorbent) was captured during this transient period. 7681

dx.doi.org/10.1021/ie400197w | Ind. Eng. Chem. Res. 2013, 52, 7677−7683

Industrial & Engineering Chemistry Research The results presented in Figure 5 are also interesting in terms of the reaction time, that is, the residence time of the sorbent in the FBC reactors that are anticipated for calcium looping systems.1 Specifically, the typical residence time of sorbent in an FBC carbonator is likely to be only several minutes (potentially shorter). Therefore, only the conversions reached by a sorbent during a short period are important from a practical point of view.43 For example, it can be seen that CO2 capture uptake after 5 min is ∼4 times higher for pellets that are doped with CaBr2 and reacted in the presence of steam than for nondoped sorbent with no steam present. This means that even clearer benefits of doping and the presence of steam are experienced if sorbents are subjected to CO2 capture cycles with shorter carbonation times than employed in this work (20 min). The CO2 capture uptakes achieved by doped pellets in the presence of steam during cycles with 20-, 10-, and 5-min carbonation times are compared in Figure 6. It can be seen that the uptakes in the initial cycles were lower for shorter carbonation times, which is expected, but these uptakes were still high given that the calcination occurred under severe conditions. However, the most important result here is that the differences for these uptakes decreased with increasing numbers of reaction cycles. From the practical point of view, this means that the sorbent activity is more stable over longer series of cycles under realistic conditions and with shorter carbonation times. A likely explanation for this phenomenon is that, with lower conversions for initial cycles, the sorbent is less sintered and therefore more active in subsequent cycles. A similar observation was made by Grasa et al.,44 who found that sorbent partially carbonated during calcination/carbonation cycles demonstrated a higher integral CO2 capture capacity in a longer series of cycles. This is also in agreement with the results of our earlier parametric study on sorbent performance,45 which showed that longer carbonation times cause lower conversions in longer series of calcination/carbonation cycles.

ACKNOWLEDGMENTS



REFERENCES

This work was partially supported by the European Community’s Seventh Framework Programme (FP7/20072013) under the GA 241302 − CaOling project, together with funding from the interdepartmental Program on Energy Research Development operated by Natural Resources Canada.

(1) Blamey, J.; Anthony, E. J.; Wang, J.; Fennell, P. S. The use of the calcium looping cycle for post-combustion CO2 capture. Prog. Energy Combust. Sci. 2010, 36, 260−279. (2) Liu, W.; An, H.; Qin, C.; Yin, J.; Wang, G.; Feng, B.; Xu, M. Performance enhancement of calcium oxide sorbents for cyclic CO2 captureA review. Energy Fuels 2012, 26, 2751−2767. (3) Rodriguez, N.; Alonso, M.; Abanades, J. C. Average activity of CaO particles in a calcium looping system. Chem. Eng. J. 2010, 156, 388−394. (4) Coppola, A.; Montagnaro, F.; Salatino, P.; Scala, F. Fluidized bed calcium looping: The effect of SO2 on sorbent attrition and CO2 capture capacity. Chem. Eng. J. 2012, 207−208, 445−449. (5) Abanades, J. C.; Grasa, G.; Alonso, M.; Rodriguez, N.; Anthony, E. J.; Romeo, L. M. Cost structure of a postcombustion CO2 capture system using CaO. Environ. Sci. Technol. 2007, 41, 5523−5527. (6) MacKenzie, A.; Granatstein, D. L.; Anthony, E. J.; Abanades, J. C. Economics of CO2 capture using the calcium cycle with a pressurized fluidized bed combustor. Energy Fuels 2007, 21, 920−926. (7) Abanades, J. C.; Anthony, E. J.; Wang, J.; Oakey, A. Fluidized bed combustion systems integrating CO2 capture with CaO. Environ. Sci. Technol. 2005, 39, 2861−2866. (8) Abanades, J. C.; Rubin, E. S.; Anthony, E. J. Sorbent cost and performance in CO2 capture system. Ind. Eng. Chem. Res. 2004, 43, 3462−3466. (9) Manovic, V.; Anthony, E. J.; Loncarevic, D. SO2 Retention by CaO-based sorbent spent in CO2 looping cycles. Ind. Eng. Chem. Res. 2009, 48, 6627−6632. (10) Grasa, G. S.; Abanades, J. C. CO2 capture capacity of CaO in long series of carbonation/calcination cycles. Ind. Eng. Chem. Res. 2006, 45, 8846−8851. (11) Chen, Z.; Song, H. S.; Portillo, M.; Lim, C. J.; Grace, J. R.; Anthony, E. J. Long-term calcination/carbonation cycling and thermal pretreatment for CO2 capture by limestone and dolomite. Energy Fuels 2009, 23, 1437−1444. (12) Sun, P.; Grace, J. R.; Lim, C. J.; Anthony, E. J. The effect of CaO sintering on cyclic CO2 capture in energy systems. AIChE J. 2007, 53, 2432−2442. (13) Abanades, J. C.; Alvarez, D. Conversion limits in the reaction of CO2 with lime. Energy Fuels 2003, 17, 308−315. (14) Fennell, P. S.; Pacciani, R.; Dennis, J. S.; Davidson, J. F.; Hayhurst, A. N. The effects of repeated cycles of calcination and carbonation on a variety of different limestones, as measured in a hot fluidized bed of determination sand. Energy Fuels 2007, 21, 2072− 2081. (15) Alvarez, D.; Abanades, J. C. Determination of the critical product layer thickness in the reaction of CaO with CO2. Ind. Eng. Chem. Res. 2005, 44, 5608−5615. (16) Li, Z.; Sun, H.; Cai, N. Rate equation theory for the carbonation reaction of CaO with CO2. Energy Fuels 2012, 26, 4607−4616. (17) Li, Z.; Fang, F.; Tang, X.; Cai, N. Effect of temperature on the carbonation reaction of CaO with CO2. Energy Fuels 2012, 26, 2473− 2482. (18) Lysikov, A. I.; Salanov, A. N.; Okunev, A. G. Change of CO2 carrying capacity of CaO in isothermal recarbonation−decomposition cycles. Ind. Eng. Chem. Res. 2007, 46, 4633−4638. (19) Manovic, V.; Anthony, E. J. Thermal activation of CaO-based sorbent and self-reactivation during CO2 capture looping cycles. Environ. Sci. Technol. 2008, 42, 4170−4174.

4. CONCLUSIONS The results presented herein, confirm that small amounts of bromides present in a CaO-based sorbent can enhance its activity for CO2 capture in calcium looping cycles in the presence of steam. It is also clear that the diffusion stage of carbonation is enhanced by the presence of bromide ions in the sorbent structure and steam in the gas mixture during calcination/carbonation cycles. Both bromide and steam improve the conversion rate individually, but their synergetic effect results in the highest CO2 capture uptakes. The effect is even more pronounced in the case of synthetic calcium aluminate pellets. Moreover, it is clear that this low halide level also helps alleviate concerns about corrosion or agglomeration in FBC systems. Finally, steam, which is nearly always present in gas mixtures to be decarbonized, should be included in future CO2 tests with synthetic materials because their observed performances appear to be very positively affected by steam.





Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: b.j.anthony@cranfield.ac.uk. Tel.: 44(01)1234 750111 x 2823. Fax: 44(0)1234 754036. Notes

The authors declare no competing financial interest. 7682

dx.doi.org/10.1021/ie400197w | Ind. Eng. Chem. Res. 2013, 52, 7677−7683

Industrial & Engineering Chemistry Research

Article

(20) Sun, P.; Grace, J. R.; Lim, C. J.; Anthony, E. J. Investigation of attempts to improve cyclic CO2 capture by sorbent hydration and modification. Ind. Eng. Chem. Res. 2008, 47, 2024−2032. (21) Li, Y.; Zhao, C.; Chen, H.; Liang, C.; Duan, L.; Zhou, W. Modified CaO-based sorbent looping cycle for CO2 mitigation. Fuel 2009, 88, 697−704. (22) Ridha, F. N.; Manovic, V.; Wu, Y.; Macchi, A.; Anthony, E. J. Post-combustion CO2 capture by formic acid-modified CaO-based sorbents. Int. J. Greenhouse Gas Control 2013, 16, 21−28. (23) Dennis, J. S.; Pacciani, R. The rate and extent of uptake of CO2 by a synthetic, CaO-containing sorbent. Chem. Eng. Sci. 2009, 64, 2147−2157. (24) Broda, M.; Muller, C. R. Synthesis of highly efficient, Ca-based, Al2O3 stabilized, carbon gel templated CO2 sorbents. Adv. Mater. 2012, 24, 3059−3064. (25) Santos, E. T.; Alfonsin, C.; Chambel, A. J. S.; Fernandes, A.; Soares Dias, A. P.; Pinheiro, C. I. C.; Ribeiro, M. F. Investigation of a stable synthetic sol−gel CaO sorbent for CO2 capture. Fuel 2012, 94, 624−628. (26) Manovic, V.; Anthony, E. J. Carbonation of CaO-based sorbents enhanced by steam addition. Ind. Eng. Chem. Res. 2010, 49, 9105− 9110. (27) Donat, F.; Florin, N. H.; Anthony, E. J.; Fennell, P. S. Influence of high-temperature steam on the reactivity of CaO sorbent for CO2 capture. Environ. Sci. Technol. 2012, 46, 1262−1269. (28) Anthony, E. J.; Lu, D.; Salvador, C. Reactivation of lime-based sorbents by CO2. U.S. Patent Application 2007/0032380 A1, Feb 8, 2007. (29) Arias, B.; Grasa, G. S.; Alonso, M.; Abanades, J. C. Postcombustion calcium looping process with a highly stable sorbent activity by recarbonation. Energy Environ. Sci. 2012, 5, 7353−7359. (30) Manovic, V.; Anthony, E. J. Steam reactivation of spent CaObased sorbent for multiple CO2 capture cycles. Environ. Sci. Technol. 2007, 41, 1420−1425. (31) Phalak, N.; Deshpande, N.; Fan, L.-S. Investigation of hightemperature steam hydration of naturally derived calcium oxide for improved carbon dioxide capture capacity over multiple cycles. Energy Fuels 2012, 26, 3903−3909. (32) Yin, J.; Zhang, C.; Qin, C.; Liu, W.; An, H.; Chen, G.; Feng, B. Reactivation of calcium-based sorbent by water hydration for CO2 capture. Chem. Eng. J. 2012, 198−199, 38−44. (33) Wu, Y.; Manovic, V.; He, I.; Anthony, E. J. Modified lime-based pellet sorbents for high-temperature CO2 capture: Reactivity and attrition behaviour. Fuel 2012, 96, 454−461. (34) Manovic, V.; Wu, Y.; He, I.; Anthony, E. J. Spray water reactivation/pelletization of spent CaO-based sorbent from calcium looping cycles. Environ. Sci. Technol. 2012, 46, 12720−12725. (35) Manovic, V.; Anthony, E. J. CaO-based pellets with oxygen carriers and catalysts. Energy Fuels 2011, 25, 4846−4853. (36) Al-Jeboori, M. J.; Nguyen, M.; Dean, C.; Fennell, P. S. Improvement of limestone-based CO2 sorbents for Ca-looping by HBr and other mineral acids. Ind. Eng. Chem. Res. 2013, 52, 1426−1433. (37) Manovic, V.; Anthony, E. J. CO2 Carrying behavior of calcium aluminate pellets under high-temperature/high-CO2 concentration calcination conditions. Ind. Eng. Chem. Res. 2010, 49, 6916−6922. (38) Florin, N. H.; Harris, A. T. Screening CaO-based sorbents for CO2 capture in biomass gasifiers. Energy Fuels 2008, 22, 2734−2742. (39) Arias, B.; Grasa, G.; Abanades, J. C.; Manovic, V.; Anthony, E. J. The effect of steam on the fast carbonation reaction rates of CaO. Ind. Eng. Chem. Res. 2012, 51, 2478−2482. (40) Chopra, O. K.; Smith, G. W.; Lenc, J. F.; Shearer, J. A.; Myles, K. M.; Johnson, I. Effect of salt treatment on sulfation and on the corrosion behavior of materials in AFBC systems. In Proceedings of the Sixth International Conference on Fluidized Bed Combustion; U.S. Department of Commerce-NTIS: Washington, DC, 1980; pp 496− 505. (41) Al-Jeboori, M. J.; Fennell, P. S.; Gonzalez, B. Sorbent enhancement through doping. Presented at the CaOling Workshop and Open Day Event, Oviedo, Spain, Apr 19, 2012.

(42) Fennell, P. S.; Al-Jeboori, M. CaO-based sorbent enhancement through doping. UK Priority Patent Application 1114105.8, Aug 16, 2011. (43) Alonso, M.; Rodriguez, N.; Grasa, G.; Abanades, J. C. Modelling of a fluidized bed carbonator reactor to capture CO2 from a combustion flue gas. Chem. Eng. Sci. 2009, 64, 883−891. (44) Grasa, G.; Abanades, J. C.; Anthony, E. J. Effect of partial carbonation on the cyclic CaO carbonation reaction. Ind. Eng. Chem. Res. 2009, 48, 9090−9096. (45) Manovic, V.; Anthony, E. J. Parametric study on the CO2 capture capacity of CaO-based sorbents in looping cycles. Energy Fuels 2008, 22, 1851−1857.

7683

dx.doi.org/10.1021/ie400197w | Ind. Eng. Chem. Res. 2013, 52, 7677−7683